1. Field of the Invention
This invention concerns superconducting materials, in general. More specifically, it relates to a method for producing superconducting materials in a continuous manner on a filament substrate. Still more specifically, it concerns a method of continuous production of superconducting wire which includes niobium-germanium produced on the surface thereof by a chemical vapor plating procedure.
2. Description of the Prior Art
In the field of superconducting materials, there is a continuous effect to discover new materials which have superconductivity and that retain such property at higher temperatures than did the earliest known such materials. Most of the materials that have been known heretofore have critical temperature characteristics that are quite restricting in that they lose the superconductivity at temperatures which are not much above the boiling point of liquid helium. Such temperatures are quite considerably below the boiling point of hydrogen which is 20.4.degree. K.
In the course of developing superconducting materials having higher transistion temperatures, there has been an intermetallic compound produced by one John R. Gavaler. It is the intermetallic compound niobium-germanium. This was found to have a superconducting transition temperature of 22.3.degree. K. However, even though this high transition temperature is very significant because of the fact that it would make feasible the use of liquid hydrogen rather than the more expensive and less abundant liquid helium, the Gavaler discovery employed a sputtering process for producing the intermetallic compound and therefore it was only applicable to a batch-type method. Consequently, it has not been found attractive for practical use, as yet.
Other know procedures for making superconducting wire have had substantial drawbacks because of the characteristics of the superconducting compounds, particularly in regard to the lack of ductility. Consequently, a majority of present superconducting devices employ superconducting wires made as composites of niobium-titanium and copper. Such composites are made by inserting small rods of niobium-titanium into copper tubes and stacking such tubes into a billet. The billet is then extruded into a rod with small diameter and then drawn into wires of appropriate size. Despite this technique being the most wide spread, such a wire is limited for some applications by its superconducting properties because the transition temperature of niobium-titanium is about 9.degree. K. which is quite close to the temperature of liquid helium as a refrigerant. Also, this compound has its superconducting properties destroyed by magnetic fields above about 10 teslas, so that it is not useful for high field magnets.
Another superconducting material is niobium-tin which has a transition temperature of about 18.degree. K. and a critical field of 21 teslas. But, this material is quite brittle, breaks easily and is difficult to handle. Furthermore, it has poor thermal conductivity which creates problems in maintaining a superconducting state. Heretofore, the best approach for employing niobium-tin superconductors has been to manufacture them in the form of a tape or ribbon composed of several layers of different materials. This requires rather complicated mechanical procedures for the manufacture, and consequently involves substantial drawnbacks.
Consequently, it is an object of this invention to teach a method for continuously producing various superconducting wires.
Another object of the invention is to teach a method for producing a superior superconducting intermetallic compound, plated onto the surface of a filament of a niobium wire substrate.